In this work, we demonstrate that the optical properties of CdSe nanocrystals (NCs) show a strong size dependence at low temperature (~10 K). The photoluminescence (PL) peak is shifted to higher energies as the growth time of synthesized CdSe NCs decreases, which can be attributed to size differences of CdSe NCs. The power-dependent PL measurements, where the PL intensities are linearly increased as a function of laser excitation powers were performed. These linearly increased PL intensities support the excitonic properties of confined states in CdSe NCs. In addition, the carrier dynamics of CdSe NCs are observed using time-resolved PL measurements. The carrier decay times are increased as the sizes of CdSe NCs are increased.

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We passivated the surfaces of CdSe quantum dots (QDs) with Z-type ligands and demonstrated enhanced emission from the QDs. We studied the effects of the ligands on the quality of the QDs and the presence of cadmium halide complexes in the CdSe QDs functionalized with carboxylic and phosphine ligands. The photoluminescence (PL) intensity of the CdSe QDs treated with Z-type ligands at 40 ∘ C for 15 min was enhanced by ~2 times compared to that of pristine CdSe QDs because of surface defect passivation. By contrast, the PL intensity of CdSe QDs treated without Z-type ligands at 40 ∘ C for 15 min decreased by ~20 % compared to that of pristine CdSe QDs because of induced surface defects. The slight changes in the PL peak position and full width at half-maximum of the CdSe QDs passivated with Z-type ligands at different temperatures can be attributed to the modification of surface properties. In addition, the slight red shift in the PL peak position of the CdSe QDs treated without ligands at 40 ∘ C for 15 min is attributed to increased QD size.